This invention relates to compression release engine brakes, and more particularly to electronic controls for such engine brakes.
As is well known to those skilled in the art, compression release engine brakes operate to temporarily convert an associated internal combustion engine from a power source to a power-absorbing gas compressor when the engine brake is turned on and the fuel supply to the engine is cut off. In general, such engine brakes operate in this way by opening the exhaust valve in the engine cylinders when the engine cylinders contain air they have compressed. For example, the engine brake may open an exhaust valve in the engine near top dead center of each compression stroke of the engine cylinder served by that exhaust valve. This allows compressed air to escape from the engine, thereby preventing the engine from recovering the work of compressing that air. (As an alternative to using a conventional exhaust valve for this purpose, the same result may be achieved by having the engine brake open a special-purpose valve that has been added to each engine cylinder. (See, for example, Gobert et al. U.S. Pat. No. 5,146,890.) Because such special-purpose valves are so much like conventional exhaust valves in this connection, it will be understood that, as used herein, terms like "exhaust valves" include both conventional exhaust valves and special-purpose valves added for use in producing compression release events. By preventing the engine from recovering the work of compressing air the engine has compressed, the engine brake enables the engine to absorb much more kinetic energy from the vehicle powered by the engine. The engine therefore becomes much more effective in slowing down or holding back the vehicle, thereby prolonging the life of the vehicle's wheel brakes and increasing vehicle safety.
Most known compression release engine brakes produce the above-described exhaust valve openings by hydraulically transferring an appropriately timed motion from another part of the engine to the exhaust valve to be opened to produce a compression release event. For example, a master piston in a hydraulic circuit in the engine brakes may be operated by an intake or exhaust valve opening mechanism of another engine cylinder or by the fuel injector mechanisms of the same engine cylinder in which the compression release event is to be produced. A slave piston in that hydraulic circuit responds to operation of the master piston by opening an associated exhaust valve to produce the compression release event.
It can be difficult or even impossible to produce optimally timed exhaust valve openings at all operating speeds, using the conventional approach described above. Many complex mechanical, hydraulic, etc., refinements have been devised to improve the compression release event timing options available to the engine brake designer. Some of these refinements work extremely well, but they have a tendency to increase the cost of the engine brake.
Recently, engine brakes have been developed which use electronically controlled valves to apply high pressure hydraulic fluid to hydraulic actuators which open associated engine exhaust valves to produce compression release events. Examples of such engine brakes are shown in Pitzi, U.S. Pat. No. 5,012,778 (Jul. 7, 1991) and Hu et al., U.S. Pat. No. 5,429,890 (Jan. 2, 1996) for Externally Driven Compression Release Retarders. More sophisticated electronic controls are needed for such brakes.
In view of the foregoing, it is an object of this invention to provide improved electronic controls for compression release engine brakes.
It is another object of this invention to provide improved electronic controls for compression release engine brakes of the type which employ electronically controlled valves for applying high pressure hydraulic fluid to hydraulic actuators when compression release events are desired.
It is a further object of the invention to provide methods of controlling electronically controlled hydraulic actuators.